1. Field of the Invention
This invention relates to constant velocity universal joints which transmit rotational motion between driving and driven shafts without changing the angular velocity, and more particularly to a novel tripod type constant velocity universal joint with modified roller races.
2. Description of the Prior Art
A tripod type constant velocity universal joint is known in the art, which comprises a spider member having three roller supporting rods extended radially from the concentrated portion thereof with an angle of 120 degrees formed therebetween, the spider member being connected to a first transmission shaft, which is one of a pair of driving and driven shafts; roller elements respectively rotatably supported on the roller supporting rods in such a manner that the roller elements are movable along the roller supporting rods, respectively; and a pot member having a cylindrical part with pairs of roller raceways which respectively receive the roller elements therebetween, the pot member being connected to a second transmission shaft which is the other of the pair of driving and driven shafts. If, in a constant velocity universal joint of this type, only the constant velocity characteristic is taken into consideration, it is preferable that the roller races (the pairs of roller raceways) are respectively extended in parallel with the rotational axis of the pot member. However, in order to decrease the size of the universal joint and to reduce the weight of the same, it is not always preferable that the roller races are in parallel with the rotational axis of the pot member. In a conventional tripod type constant velocity universal joint put to practical use, in order to reduce the size and weight, the top end portions of the roller races are slightly bent toward the rotational axis of the pot member. That is, they are subjected to so-called "one side modification." This tripod type constant velocity universal joint having its roller races subjected to one side modification is small in size and light in weight when compared with a tripod type constant velocity universal joint having its roller races not modified. However, the former universal joint suffers from a disadvantage that its constant velocity characteristic is impaired.
Namely, the quantities of nonconstant velocity in the rotation of the tripod type universal joint are decided by adding two values obtained by multiplying each difference of pitch radiuses of the portions at which two adjacent roller elements are respectively located between pairs of roller raceways by each value represented by a trigonometric function. In the original tripod type universal joint not having one side modification, as the differences of pitch radiuses of two adjacent roller elements which are respectively located in pairs of roller raceways provided in parallel with respect to the rotational axis of the pot member is zero, the quantities of nonconstant velocity (velocity fluctuation) are therefore also zero.
On the other hand, in the tripod type universal joint having said one side modification, the differences of the pitch radiuses of the portions at which two adjacent roller elements are respectively located in the pairs of roller raceways are increased. For example, one roller element is located at a parallel portion of a pair of roller raceways, and the other roller element is located at a bent portion thereof, so that the quantities of nonconstant velocity are increased according to the increase of the differences.
In order to reduce the size of the three roller type joint relative to the previous one of this type and to provide increased torque carrying capacity, according to Wahlmark (U.S. Pat. No. 3,877,251), it was found that for efficient operation with smallest joint size for given torque capacity, the ratio (R.sub.o /r) of torque arm (R.sub.o) to track radius (r) should be maintained within the range of 0.75 to 0.90.
In U.S. Pat. No. 3,877,251 to Wahlmark, since the off-set quantity (i.e., R.sub.o /r) is maintained within the range of 0.75 to 0.90, an approach quantity of the roller races along an arc lines at both ends thereof is large. Accordingly, in Wahlmark the quantity of nonconstant velocity in the universal joint is increased, for example the quantity of nonconstant velocity is 0.0375 in the plane cross-angle .gamma.=37.degree. or 0.0693 in the plane cross-angle .gamma.=41.degree., so that the constant velocity characteristic thereof will be lowered without being maintained. Furthermore, as in Wahlmark, the torque arm is 1.25 inches and the track radius is 1.50 inches.
The configuration of the roller races (pairs of roller raceways) of a tripod type constant velocity universal joint greatly affects the general performance thereof. Accordingly, it is considerably important to modify the configuration of the roller races, in order to improve the general performance of the tripod type constant velocity universal joint.